18. \( \left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right)\left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right) \)

Calculate or simplify the expression \( (3-x/3)*(3+x/3)*(3-x/3)*(3+x/3) \). Simplify the expression by following steps: - step0: Solution: \(\left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right)\left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right)\) - step1: Subtract the terms: \(\frac{9-x}{3}\times \left(3+\frac{x}{3}\right)\left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right)\) - step2: Add the terms: \(\frac{9-x}{3}\times \frac{9+x}{3}\times \left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right)\) - step3: Subtract the terms: \(\frac{9-x}{3}\times \frac{9+x}{3}\times \frac{9-x}{3}\times \left(3+\frac{x}{3}\right)\) - step4: Add the terms: \(\frac{9-x}{3}\times \frac{9+x}{3}\times \frac{9-x}{3}\times \frac{9+x}{3}\) - step5: Multiply the terms: \(\frac{\left(9-x\right)\left(9+x\right)}{9}\times \frac{9-x}{3}\times \frac{9+x}{3}\) - step6: Multiply the terms: \(\frac{\left(9-x\right)^{2}\left(9+x\right)}{27}\times \frac{9+x}{3}\) - step7: Multiply the terms: \(\frac{\left(9-x\right)^{2}\left(9+x\right)\left(9+x\right)}{27\times 3}\) - step8: Multiply the terms: \(\frac{\left(9-x\right)^{2}\left(9+x\right)^{2}}{27\times 3}\) - step9: Multiply the terms: \(\frac{\left(9-x\right)^{2}\left(9+x\right)^{2}}{81}\) - step10: Simplify: \(\frac{\left(81-x^{2}\right)^{2}}{81}\) - step11: Expand the expression: \(\frac{6561-162x^{2}+x^{4}}{81}\) The expression \( \left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right)\left(3-\frac{x}{3}\right)\left(3+\frac{x}{3}\right) \) simplifies to \( \frac{6561-162x^{2}+x^{4}}{81} \).